In metal machining operations, cutting fluids or coolants are widely used to wash away chips, reduce generated heat and to reduce the friction between a tool and a chip. In the past, the coolant has either been turned on and off manually by an operator or left running during periods when the tool is not engaged with a workpiece and coolant flow was unnecessary. The rapid cutting speeds used in modern high production machining operations accentuate the need for cutting fluids or coolants, and the modern machines frequently use coolant under high pressure and flow rates. The high pressure flow has the undesirable effect of splashing and misting areas adjacent to the machine with coolant during periods when the tool is not engaged with the workpiece. Inasmuch as the cutting fluid is not required until the tool engages the workpiece, and the actual cutting operation commences, it would be desirable to delay the high pressure flow until the fluid is actually needed and to thereby eliminate the coolant waste and inconvenience of prior art machines.
Delaying high pressure coolant flow has an additional advantage when tools with internal cutting fluid passages are used. In these tools, coolant flows through passages in a working head of the machine and through the cutting tool. The high pressure cutting fluid pushes against the tool and may dislodge it from a tool holder in some circumstances. Delaying assertion of this high pressure fluid force until the tool engages the workpiece insures that the force resulting from the fluid pressure is opposed by the engagement force of the workpiece and the possibility of tool dislodgement is reduced.